Re: [PATCH] PM / suspend: measure the time of filesystem syncing

From: Rafael J. Wysocki
Date: Tue Feb 12 2019 - 18:27:04 EST


On Wed, Feb 13, 2019 at 12:21 AM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
>
> On Wed, Feb 6, 2019 at 4:57 PM Harry Pan <harry.pan@xxxxxxxxx> wrote:
> >
> > This patch gives the reader an intuitive metric of the time cost by
> > the kernel issuing a filesystem sync during suspend; although developer
> > can guess by the timestamp of next log or enable the ftrace power event
> > for manual calculation, this manner is easier to read and benefits the
> > automatic script.
> >
> > v2: simplify the variables, apply the simplest form of ktime API.
> >
> > Signed-off-by: Harry Pan <harry.pan@xxxxxxxxx>
> > ---
> > kernel/power/suspend.c | 7 ++++++-
> > 1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
> > index 0bd595a0b610..87c0073f0c9d 100644
> > --- a/kernel/power/suspend.c
> > +++ b/kernel/power/suspend.c
> > @@ -550,6 +550,8 @@ static void suspend_finish(void)
> > static int enter_state(suspend_state_t state)
> > {
> > int error;
> > + ktime_t start;
> > + unsigned int elapsed_msecs;
>
> You only need these two if CONFIG_SUSPEND_SKIP_SYNC is set, ->
>
> >
> > trace_suspend_resume(TPS("suspend_enter"), state, true);
> > if (state == PM_SUSPEND_TO_IDLE) {
> > @@ -570,9 +572,12 @@ static int enter_state(suspend_state_t state)
> >
> > #ifndef CONFIG_SUSPEND_SKIP_SYNC
>
> -> so I would change this to
>
> if (IS_ENABLED(CONFIG_SUSPEND_SKIP_SYNC)) {

if (!IS_ENABLED(CONFIG_SUSPEND_SKIP_SYNC)) {

that is (missing "!").

> ktime_t start;
> unsigned int elapsed_msecs;
>
> > trace_suspend_resume(TPS("sync_filesystems"), 0, true);
> > + start = ktime_get();
>
> Why don't you do this after printing the message below?
>
> > pr_info("Syncing filesystems ... ");
> > ksys_sync();
> > - pr_cont("done.\n");
> > + elapsed_msecs = ktime_to_ms(ktime_sub(ktime_get(), start));
> > + pr_cont("(elapsed %d.%03d seconds) done.\n", elapsed_msecs / 1000,
> > + elapsed_msecs % 1000);
>
> Use MSEC_PER_SEC here.
>
> > trace_suspend_resume(TPS("sync_filesystems"), 0, false);
> > #endif
> >